Phase modulation system



Dec. 1, 1942. r J. PLEBANSKI ,3 5

' PHASE mommmlon SYSTEM Filed June 20, 1940 2 Sheets-Sheet 1 FIG. 1.-

IRVENTOR BY 1025/ PLEBAMSK/ ATTORNEY 1942- J. PLEBANSKI I 3 2,303,863

I PHASE IVIQDULA'I.ION SYSIEM I Filed June 20, 1940 2 Sheets-Sheet 2 F/G .2 FIGS).-

i HMPLIF/EK ATTORNEY frequency wave.

An object of the invention is to providea novel Patented Dec. 1,

' rnasa monum'rion SYSTEM Jozef Plebansk'i; Warsaw, Poland, assignor to Badio Patents Corporation, -a corporation, oi New York Application June 20.1940, Se 1 No. stress In Poland August 2 19 37 2 Claims. (Cl. 1179-1715) w This application is a continuation in part of my application Serial No. 224,061, filed August 10, 1938, entitled Electric controlsystem.

--'I'he'present invention relates to radio systems and more particularly to an improved system for and a method of phase modulating 'a high frequency carrier wave in accordance with a signal phase modulating system and a method of operatingsame which is both simple in design and characterized by increased efllciency compared with phase modulating systems-known in the prior art.

Another object is to effect a phase modulation of a high frequency carrier wave by the employment' of purely electrical means. that is, without reigning devices having mechanically moving pa s. V

The above and further objects and advantages energized by the carrier and modulating poten-' tials by connecting the primaries of transformers M, l5, and i8, it, it in serieswith the master oscillator It and the source of modulating potential (terminal posts ll), respectively. Any other excitation such as parallel connection or mixed connection of the grids to the carrier and modulating signal sources may be employed as will be readily understood. The grids of the tubes of the invention will become more apparent from a the following detailed description taken with reference to the accompanying drawings forming part of this specification and wherein;

' Fi ure l is a circuit diagram for a radio transnutter embodying a phase modulating system 210- cording to the invention,

Figures 2 and 3 are graphs explanatory of the function and operation of the system according to Figure 1. a 3

Figure 4 is a circuit diagram of a simplified phase modulation system embodying the principles of the invention, and

Figure 5 is a graph explanatory of the function of Figure 4.

Like reference .characters identify like part in the difierent views of the drawings.

Referring to Figure 1, items IE, it and i2 represent electron discharge tubes shown as triodes amplifiers but which, as will be'understood.

may be oi any suitable type well known in the art; The control grids of all three tubes are simultaneously excited by a carrier frequency potential supplied by a suitable source such as a master oscillator I3 and impressed upon the grids in any suitable manner such as by way 01 tuned high frequency transformers 14, [Band l8,re-

spectively, as shown in the example illustrated. The control grids of the tubes i0, Hand i2 are additionally excited by a modulat ng potential scribed in said patent, in a twin resonant circuit id, It and I2 are suitably biased (steady gridbias) in a manner to be described presently such as by the aid of biasing batteries 2i and M or network 22 comprising a resistance shunted by a condenser inserted in the cathode-to-ground leadsin a manner 'well known. The output of tube to is applied by way of coupling coil 25 to a resonant circuit comprising an inductance coil 25 shunted -by a condenser 2'! having in series therewith a coupling coil 8!. The tubes and it are excited by the modulating potential in anti-phase relation or push-pull by proper connection of the primary windings of the modulating transformers i9 and Eli, respectively. The outputs of the tubes it and 82 are combined in push-pull relation by applying in a known manner the positive anode potential for the tubes to the center tap of the primary winding 28 of a common output transresonant circuit together with a condenser 30 having in series therewith a coupling coil 32.

The resonant circuits 28-21-3l and 2 tl32 are tuned tothej carrier frequency and are reactively coupled with each other,v in

the example shown through the coupling coils 3i and 82 being in inductive coupling ;relation with each other. By suitable design of the circuit con- .stants this resonant circuit arrangement constitutes a phase shifting system of the type disclosed in greater detail in my U. S. Patent No. 2,172,107 issued September 5, 1939. If, as deof this type comprising a pair of reactively coupled resonant circuits both circuits are excited separately by signals of like (resonant). frequency,

supplied from a suitable source such as from the output of a microphone circuit or the like and impressed upon the grids byway of low frequency transformers l8, l9. and '26, respectively. In the then the time phase position of the current or potential developed in either circuit will be dependent upon the amplitude relation of the signals or potentials impressed upon the circuits. Thus; if the circuits are designed in such a manner that the non-reactive (ohmic or loss) impedances of both circuits are alike and equal to'the mutual coupling impedance between the circuits, the currents developed in the circuits by potentials of:

like amplitude'separately impressed upon'the cir- ,eXample shown the grids of tubes l0, ll, l2 are cults will have a relative phase diiierence of former having a secondary 29 forming a further I 2 v 2,808,868 I I resonant circuit 20-10-32} Thus, with a modufrom each other. If the relative amplitude of the signal potentials impressed upon one circuit varies in either direction, the phase differencebetween the currents developed in the circuits will 4 become greater or less, respectively, than the normal 90 phase relation, the relative phase variation being proportional to the relative amplitude stantially equal amplitude havinga phase varying in accordance with the original amplitude variation. f

According to the present invention, thenormal lating potential simultaneously-impressed upon the grids of all three tubes, n is seen that the are in phase quadrature whereby the circuit or steady grid bias for the tubes I0, H and I2 is adjusted in such a manner as to obtain a diflerential variation of the carrier current amplitudesln the circuits 262'|-3i and 29-30--32 substantially according to a sine and cosine function, respectively, in such a manner as to convert the amplitude modulations of a modulating signal applied to terminals I1 into corresponding phase variations of the currents in the resonant circuits 262|--3l and 29-30-32. .The phase modulated signal energy developed in one of the resonant circuits is then applied by way of coupling condenser 33 to a power amplifier 34 which latter feeds a utilization circuit such as an antenna 38 through a coupling transformer 35. If

. desired, a frequency multiplication arrangement rent I in the output of an amplifying tube,

plotted as a function of the grid potential e. As is seen,,the current I increases gradually starting at a predetermined negative grid potential Ez) as the grid potential becomes less negative and finally assumes positive values. At a definite positive grid potential (+E1) the cur-. rent I reaches a maximum and thereafter begins to fall as the grid is made more positive to again become zero at a definite positive grid bias (+Es) when all the electrons emitted by the cathode are 29-.3d-32 is normally, i.'e.with the modulating potential being equal to 'zero, excited from the circuit 26-21-3! only'and the phase of theoscillating current set up in the circuit 2l3l 32- will vary in either direction in proportion to positive and negative values of the modulating potential and between limits determined by the maximum amplitudes of the latter.

In the example shown t he amplitudes of the modulating. potential m vary between limits +eo and e1 corresponding to like values oi' the current I in both resonant circuits, in, which case the phase swing or deviation will be 90 in both directions. Any other phase range or depth of phase modulation may be employed to suit existing requirements. Actually a system as described and adjusted according toFigur 3 will enable a full maximum phase deviation of 180 in both directions.

If only a small phase modulation range or deviation, say 40 or less is desired, such as employedin the initial stage of present day frequency modulation transmitters, the system may be greatly simplified as shown in Figure 4 which differs from Figure 1 in that tube l2 and its associated input and output'circuits are omitted and the resonant circuit 29 2M: is energized solely by the output of tube II. By biasing tube It) positively by a potential +E and by biasing v tube II y p t ntial +E5 according to Figure operat'ing characteristics D and E with respect to acommon zero point 0 are obtained as shown I in Figure 5. As seen from the latter, when the modulating potential m is zero the currents I impressed upon both resonant circuits are ,equal' resulting in a 90 phase relation; between the currents. As the modulating potential increases in a positive or negative direction, the relative increase or decrease, respectively, of the normal attracted by the grid and no current is passed to e theplateor anode. Curve A in Figure 2 equals with sufllcient approximation a sine or cosine half wave and this fact is made use of by the invention topbtain a differential amplitude varia' tion of the carrier currents developed in the resonant circuit 28-21-3l and 28-30-32 in accordance with the modulating signal variations, to effect a corresponding phase modula- (90) phase relation. In this manner a phase I modulation with a maximum depth or deviation of 90 in either direction. from the normal phase position may be effected in a simple and most efficient manner.

cult arrangements shown and disclosed herein tion as will beunderstood from the-above.- 1 By applying a bias to tube III in Figure 1 equal to +E1 and similarly-biasing the tubes and I! by potentials E2 and +E3, respectively, asshown in As will be evident from the above the invention is not'limited to the specific details and c'irtor illustration but that modifications and variations may be resorted to diflering from the spe ciflc embodimentshown in accordance with the broaderscope and spiritof t invention. The.

*a source of carrier current to be modulated,

means for simultaneously impressing-potential 7 irom said source uponthe grids of said devices, a

l. A phase modulating system comprising three first resonant circuit tuned to the frequency of said source and fed from the output of the first of said devices, a second resonant circuit also tuned to the frequency of said source and connected to the outputs of the remaining discharge devices in push-pull, means for simultaneously impressing modulating potential upon the grids of said devices, the modulating potentials impressed upon the grids of said push-pull connected devices being of opposite polarity, further means for applying steady bias potential to-the grids of tial upon the grids of said devices, the modulating said devices, the steady bias of each of said pushpull connected devices being below and above, respectively, the steady bias of said first device, and mutual reactive coupling means between said first and second resonant circuit, and a utilization circuit energized from at least one of said resonant circuits.

2. A phase modulating system comprising three electron discharge devices, each comprising a cathode, an anode and at least one grid electrode,

a a source of carrier currentto be modulated,:

means for simultaneously impressing potential from said source upon the grids of said'devices, a

potentials impressed upon said push-pull connected devices being of opposite polarity, means for applyingsteady bias to the grids of said devices, the steady bias of each of said push-pull connected devices being above and below, respectively, the steady bias of said first device, and mutual inductive coupling means between said resonant circuits, said couplingmeans and the constants of said resonant circuits being designed so as to cause the alternating currents in said. resonant circuits to be of substantially constant amplitude and time'phase varying in accordance with said modulating potential, and a utilization circuit energized from at least one of said resonant circuits. g

JOZEF PLEBANSH. 

